A solid electrolytic capacitor has a small size, a large capacity and a low equivalent series resistance (ESR). Thus, the solid electrolytic capacitor is used at the periphery of the CPU in a personal computer. The solid electrolytic capacitor as described above has a capacitor element and a pair of external terminals. The capacitor element has a base body composed of conductive material, a dielectric film formed on this base body, a solid electrolyte layer formed on this dielectric film, and a collector layer formed on this solid electrolyte layer. The pair of external terminals is electrically connected to the base body and the collector layer, respectively.
The collector layer has a carbon layer formed on the solid electrolyte layer, and a silver paste layer formed on this carbon layer. The silver paste layer is formed by kneading silver particles having a peak size of about 1 μm, epoxy resin, and curing agent for example. In recent years, approaches are suggested to reduce the contact resistance between the silver paste layer and the carbon layer to thereby reduce the ESR of the electrolytic capacitor. As one of the approaches, mixing the silver paste layer with small silver particles having a peak particle diameter of 1 to 100 nm to improve the contact with the carbon layer is proposed (e.g., Patent Literature 1).
The silver paste layer including small silver particles provides a reduced contact resistance with the carbon layer. Thus, the silver paste layer can have a reduced thickness with the same amount of silver. However, the silver paste layer having a reduced thickness causes a shorter oxygen permeation path. Thus, the solid electrolyte layer is increasingly oxidized and deteriorated with time passage, or thermally-oxidized, thus resulting in an increased ESR.